This invention relates to optical connection arrangements, and is particularly concerned with an arrangement for facilitating modifications to optical connections during operation of an optical communications system which for example uses wavelength division multiplexing (WDM).
It is known to provide a WDM optical communication system, referred to below for brevity simply as an optical system, in which two or more optical channels are carried on a single optical fiber, each channel comprising an optical signal at a respective wavelength. At any node in the optical system, it may be desired to terminate one or more of the channels, for which purpose it is known to provide an optical add/drop multiplexer (optical ADM, or OADM). An OADM typically comprises one or more optical channel filters and/or one or more optical band filters, where an optical band comprises a plurality of optical channels to be dropped and added. Optical channel and band filters are well known in the art and need not be described here.
The use of OADMs to drop and add individual optical channels or bands provides the advantage that the node-to-node optical connectivity of the optical system can be different from the physical connectivity of the optical fibers used to carry the channels. For example, the optical fibers may extend between adjacent nodes of an optical system, whereas the optical connectivity can be such that nodes can be selectively bypassed by some channels, depending upon the optical filters provided at the nodes. Consequently, each node in such an optical system can have an OADM with a set of optical filters that are customized for that node.
As an example of this, an optical system may comprise a ring of four nodes A-D with optical fibers between adjacent nodes to provide bidirectional communication of optical signals between the adjacent nodes using three optical channels (i.e. wavelengths) 1-3. A full mesh optical connectivity can be provided among all of the nodes A-D if all of the nodes drop and add channel 1, nodes A and C also drop and add channel 2, and nodes B and D also drop and add channel 3.
Such a process of dropping and adding specific wavelengths or wavebands at respective nodes is referred to as wavelength or waveband routing.
Typically, an optical system using wavelength or waveband routing is initially deployed with different optical filters at the respective nodes, and for cost reasons only as much equipment is installed as is necessary to meet actual or short-term forecasted traffic requirements.
Over time, however, it may become necessary to modify such an optical system to meet changing requirements, for example to provide additional channels or to change the wavelength or waveband routing. Such modifications typically involve identification and disconnection of optical fibers at the nodes, addition or replacement of OADMs and/or other components such as optical transmitter and receiver cards, optical amplifiers, and dispersion compensation modules, and reconnection of the optical fibers, these steps being necessary individually for each node.
The disconnection and reconnection of optical fibers interrupts traffic for all nodes communicating via the respective fibers. In optical systems with protection switching, a protection switch can be forced to route traffic around an optical fiber to be disconnected. While this can reduce the adverse effects of modifications on traffic having the highest priority for protection, it nevertheless reduces the traffic capacity of the optical system, and results in the optical system having reduced or no protection resources against an actual fault that may occur during the modification process. This disadvantage is exacerbated by the fact that similar steps must be carried out at each node, necessitating multiple forced protection switches and an excessive time during which the optical system has reduced capacity and reduced protection resources.
In addition, the density of a typical optical system and the similar appearance of different optical fibers tend to make the manual task of sorting and identifying optical fibers to be disconnected and reconnected time consuming, expensive, and prone to errors. Furthermore, the fiber handling itself can lead to fiber damage, for example increased fiber losses due to micro-bending, and increases risks of obtaining dirty optical connections, so that operating margins of the optical system may be reduced, and consequent problems may arise at the time of the modifications or subsequently.
Consequently, there is a need to provide an improved optical connection arrangement, which can enable modifications such as those discussed above to be made in a manner to reduce or avoid these disadvantages.
According to one aspect of this invention there is provided an optical connection arrangement comprising: a plurality of optical ports each comprising at least two optical connections for respectively supplying an optical signal to and receiving an optical signal from an optical component coupled to the respective port; an optical signal input; an optical signal output; and at least one optical switch coupled to the optical signal input, the optical signal output, and the plurality of optical ports, the optical switch being controllable to provide an optical path from the optical signal input to the optical signal output selectively via none, one, or at least two of the plurality of optical ports.
In different embodiments of the invention, such connection arrangements can be combined in various series and/or parallel combinations, and the at least one optical switch can comprise 1xc3x972 and 2xc3x972 optical switches, or one or more Nxc3x97N optical switches where N is an integer greater than 2.
In particular embodiments of the invention, each optical port has an optical connection to one of two optical outputs of a preceding optical switch stage, and an optical connection to one of two inputs of a following switch stage, the optical switch stages constituting said at least one optical switch, a first one of said optical switch stages having an optical input coupled to said optical signal input and a last one of said optical switch stages having an optical output coupled to said optical signal output, the arrangement further comprising an optical coupling from another of the two optical outputs of each said preceding optical switch stage to another of the two inputs of the respective following switch stage for optically bypassing the respective optical port, each optical switch stage having two optical connection states between its input(s) and its output(s), the optical switch stages being controllable to include selectively each optical port in, or selectively exclude it from, an optical path from said optical signal input to said optical signal output.
Another aspect of the invention provides an optical add/drop multiplexer (OADM) arrangement comprising: an optical connection arrangement in an optical path, the optical connection arrangement comprising at least one optical switch and a plurality of optical ports each of which can be selectively included in the optical path or bypassed by control of said at least one optical switch, the optical ports each being arranged for coupling of an OADM thereto so that different OADMs can be coupled each to any of said plurality of optical ports; and at least one OADM optically coupled to a respective optical port of the optical connection arrangement.
A further aspect of the invention provides a method of modifying optical couplings of one or more optical components to an optical path, comprising the steps of: providing in the optical path an optical connection arrangement having a plurality of optical ports each of which can be selectively included in the optical path or bypassed by control of at least one optical switch of the optical connection arrangement; changing optical couplings of at least one optical component to a respective optical port while the optical connection arrangement is controlled to selectively bypass the respective optical port; and subsequently controlling the optical connection arrangement to selectively include the respective optical port and said optical component in the optical path.